This invention pertains to the art of fluid control devices and more particularly to fluid control valves.
The invention is particularly applicable to a so-called plug valve and will be described with particular reference thereto. While the valve is particularly applicable to liquid systems, it will be appreciated that the invention may have application to other environments.
Plug valves of various types and styles are known in the art. Basically, these valves include a valve body having a generally cylindrical plug receiving opening therein adapted to closely receive a plug member. This plug member includes a flow passage extending therethrough and is selectively rotatable in the valve body for purposes of moving the flow passage into and out of alignment with the valve body inlet and outlet passageways. Seal means are disposed at any open end area or end areas of the plug member for preventing fluid by-pass outwardly from the valve body receiving opening. In some cases, seal means have also been provided in the plug member to sealingly surround at least the valve body inlet when the valve is moved to a closed condition. In addition, some prior plug valve designs have incorporated various relief opening configurations to facilitate fluid pressure relief when the valve is moved to the closed position. Still other prior plug valves have incorporated coatings or the like on the plug member for reducing the force requirements in rotating the plug member between valve opened and closed positions.
While some prior plug valves have proved successful for selected applications, most have had certain undesirable operational characteristics. These characteristics include valve leakage, complexity of valve design and assembly, blow-out of sealing members when the valves are moved between opened and closed positions, difficulty of movement between valve positions, abrading of the seal members during valve assembly, disassembly and operation, and limitations as to the types of fluid systems in which they could be used. Accordingly, it has been desired to develop a plug valve construction which would overcome the aforementioned particular difficulties and the subject invention is believed to successfully meet these needs.